The present invention disclosed herein relates to a mobile transmitter, and more particularly, to a mobile transmitter capable of operating in at least two transmit (TX) modes and a transmitting method thereof.
The present invention has been derived from a research undertaken as a part of IT R & D program of the Ministry of Information and Communication and Institution of Information Technology Association (MIC/IITA) [2005-S-017-03], Integrated development of ultra low power RF/HW/SW SoC.
The requirements of a mobile terminal include a low power, a low price, a small size, a high data rate, and a soft defined radio (SDR) function. In terms of power amplifier design, the use of a complementary metal-oxide semiconductor (CMOS) process is preferable to the use of a GaAs process for achievement of the small size and the low price. Also, in the mobile terminal, the number of external SMT (surface mounting technology) components need be reduced and as many components as possible need be built in a main RF (radio frequency) chip.
A high-linearity power amplifier is required for design of a high-data-rate transmitter. However, because a CMOS power amplifier has a lower linearity than a GaAs power amplifier, it is necessary to provide transmission structures for addressing the lower linearity of the CMOS power amplifier. One of such transmission structures is a polar transmitter. An example of the polar transmitter is disclosed in U.S. Pat. No. 6,892,057 entitled “METHOD AND APPARATUS FOR REDUCING DYNAMIC RANGE OF A POWER AMPLIFIER” and issued to Nilsson et al. on May 10, 2005.
In general, a polar transmitter processes an amplitude signal R(t) and a phase signal θ(t) in a separate manner. For example, the amplitude signal is input to a bias circuit of a switching power amplifier in the polar transmitter, while the phase signal is input to a signal input unit of the switching power amplifier. Thereafter, the amplitude signal and the phase signal are amplified and combined by the switching power amplifier. The maximum range of the amplitude signal input to the bias circuit of the switching power amplifier is limited by the level of a power source voltage. That is, the polar transmitter has a small dynamic range. Therefore, the polar transmitter is used in communication systems such as Global System for Mobile Communications (GSM) systems in which an amplitude signal of a TX signal is constant or an output dynamic range is small. However, the use of the polar transmitter is restricted in communication systems such as Wideband Code Division Multiple Access (WCDMA) systems that have a high dynamic range. Thus, a WCDMA direct-conversion transmitter uses a class-AB or class-A linear power amplifier. However, due to its low power efficiency, the linear power amplifier requires a higher power consumption than the switching power amplifier.